Actuators are used in various applications where there is a need to prevent back rotation due to the force of the load on the actuator. No-back brakes are known in the art e.g. as described in U.S. Pat. No. 2,874,579, U.S. 3,269,199 and U.S. 3,583,248.
Conventional no-back brake mechanisms comprise an arrangement of pawls and ratchets which permit a limited degree of relative axial movement of the actuator components (e.g. a ball screw and brake disk) and the no-brake action depends on friction. Problems can arise in the effectiveness of the no-back brake due to non-ideal coefficients of friction and/or wear of the components. Ratchet wheels and pawls are difficult to manufacture and with conventional carbon disks there is a large dispersion of friction coefficient and surface polishing effects. Ratchets and pawls have to be manufactured to accurate tolerance levels.
One solution to these problems has been to provide an alternative no-back brake mechanism comprising a brake ring comprising an annular frame or cage with openings for a plurality of rollers arranged to determine the overall coefficient of friction of the system. Such a mechanism is described, e.g. in U.S. Pat. No. 6,109,415 which comprises an arrangement of rollers at a skew angle relative to a diameter intersecting the centre of the roller. The skew angles are set and fixed for the desired coefficient of friction and braking effect.
The present disclosure provides an improved no-back brake mechanism that overcomes the disadvantages of conventional mechanisms.